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giosif:
Hi,

Congrats on resurrecting your multimeter and I hope it serves you for a long time!
About the baud rate, I've used the info on the page at the below link to determine unknown rates:
https://www.kumari.net/index.php/random/37-determing-unknown-baud-rate

HTH
MihaiV:
Hello,

Does the MSP430 check the analog 5V regulator and the voltage reference or just use it as external reference? My unit enables the 5v regulator but it shuts down immediately (photo in a previous post). I have not seen anything related to power coming from the analog side to any pin or other component near the MSP. My unit displays the start screen ("Fluke true rms....") but instead of measurements it displays a dark screen). Dark screen appears when the led turns off.
Towlerar:

--- Quote from: MihaiV on October 20, 2021, 08:34:03 pm ---Hello,

Does the MSP430 check the analog 5V regulator and the voltage reference or just use it as external reference? My unit enables the 5v regulator but it shuts down immediately (photo in a previous post). I have not seen anything related to power coming from the analog side to any pin or other component near the MSP. My unit displays the start screen ("Fluke true rms....") but instead of measurements it displays a dark screen). Dark screen appears when the led turns off.

--- End quote ---

As far as I am aware, the MSP430 only checks the 2.5V reference voltage level. It's more likely that the MSP430 is shutting down the 5V rail as you stated. However, the 2.5V voltage reference IC that the MSP430 monitors (U42) is fed from the 5V regulator. So if there is no 5V, there's no reference voltage.

If everything seems normal with the regulators, I would also recommend checking the UART output from the MXS IC (U26). An easy point to tap into is the unpopulated J5 at the top of the PCB. Pin 3 is TX on U26, Pin 1 is RX on U26, Pin 2 is GND and the baud rate is 115200,8,1,N. This should give you some debug info and may give you insight as to why the unit is not completing booting. Also, if the rotary switch is dirty, not making good contact, or is in an invalid rotation, you also won't get any measurements on the screen after booting.
MihaiV:
Hi Towlerar,

The 5V regulator is indeed disabled by the MSP. In a previous post there is a scope capture with it. I also checked the UART output and it shows a clean entry.

With a few precautions, I powered the 5V rail from a different source, after powering the rest of the meter, and there were no problems with the current consumption or voltage outputs. 5V was clean and so was the reference. A quick check with a thermal camera did not show any component warming up. But the behavior remained the same, meaning that it was not expecting something from the analog side.

Another thing I checked was the SPI bus between the MXS and MSP. I managed to see the MISO and MOSI signals. When powered and turned on, in the gray screen state, i can see some messages being sent by the MSP, most likely a shut-down command, but nothing happens. Perhaps that ball under the BGA (or even a via) is cracked. I will return with some scope prints with the messages.

By the way, I had to change the MXS crystal because there was no oscillation on one side of it. The chip was driving but the crystal was not resonating. After changing it with something from my junkbox is started oscillating strong and clean (see post 171 at page 7).

I assume that the crystal was broken due to a strong mechanical shock, so there may be a cracked ball somewhere. I already reflowed it once, but to no success. What else could i check?
Towlerar:

--- Quote from: MihaiV on October 24, 2021, 07:05:39 pm ---Hi Towlerar,

The 5V regulator is indeed disabled by the MSP. In a previous post there is a scope capture with it. I also checked the UART output and it shows a clean entry.

With a few precautions, I powered the 5V rail from a different source, after powering the rest of the meter, and there were no problems with the current consumption or voltage outputs. 5V was clean and so was the reference. A quick check with a thermal camera did not show any component warming up. But the behavior remained the same, meaning that it was not expecting something from the analog side.

Another thing I checked was the SPI bus between the MXS and MSP. I managed to see the MISO and MOSI signals. When powered and turned on, in the gray screen state, i can see some messages being sent by the MSP, most likely a shut-down command, but nothing happens. Perhaps that ball under the BGA (or even a via) is cracked. I will return with some scope prints with the messages.

By the way, I had to change the MXS crystal because there was no oscillation on one side of it. The chip was driving but the crystal was not resonating. After changing it with something from my junkbox is started oscillating strong and clean (see post 171 at page 7).

I assume that the crystal was broken due to a strong mechanical shock, so there may be a cracked ball somewhere. I already reflowed it once, but to no success. What else could i check?

--- End quote ---

It seems to me that since you have a clean boot-up (based on your screen capture) that the issue is likely not with the MXS, MSP, or Flash. The problem could be with bad sectors in RAM - I'm not sure how involved RAM is in the regular operation of the meter vs. simply data logging.

My fear is that there is a problem with U9, the measurement processor, which is a Fluke branded item. I'm not sure whether or not that part is available. You could check the SPI comms between the MSP and U9. On the MSP430, the following pins are SPI to the measurement processor - 63 CS, 50 SDI, 48 SCK. There is also a reset pin which comes from pin 51 on the MSP.

Since the MSP is looking for a valid rotation of the rotary switch, and you've verified that it's in a valid rotation and clean, try checking the resistor ladder it uses for determining which position it is in. R30-R35, R40-44 are used as a large resistor divider, each going to a switch position to tell the MSP what position the switch is in. I would make sure all of those values are good.
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